Abstract: An oil filter assembly for an engine of an outboard motor includes a base having a high-pressure inlet port, a filter-mounting interface for receiving a filter, and a drain-back port for receiving a drain-back insert of the filter. The base includes an engine-mounting interface for mounting the base to the engine, which includes a high-pressure outlet port and a low-pressure outlet port providing oil to the engine. The base provides fluid communication between the high-pressure inlet port and an inlet side of the filter and between an outlet side of the filter and the high-pressure outlet port when the filter is installed and the drain-back insert is within the drain-back port. The base provides fluid communication between the drain-back port and the low-pressure outlet port when the drain-back insert is not within the drain-back port. A clean oil fill passageway is in fluid communication with the low-pressure outlet port.